Device and method for removing volatile components from polymer solutions

ABSTRACT

A device and process for the removal of volatile constituents from polymers is disclosed. The device entails a container having an inlet for a polymer solution, an outlet for the volatile components, an outflow for the polymer from which the volatile components have been removed and a heat exchanger. The heat exchanger is characterized in that it contains a plurality of specially structured channels.

FIELD OF THE INVENTION

This invention relates to a device and a process for the removal ofvolatile constituents from polymers, in particular for vaporisingvolatile components from polymer solutions by indirect heat exchange.The device has at least one container with an inlet for the polymersolution and outlet for the volatile components and an outflow for thepolymer from which the volatile components have been removed, and a heatexchanger with a plurality of channels, which form a heat exchange zone,wherein the channels have a length of 1.0 to 40 cm, a height, constantover the length thereof, of 1.3 to 13 mm and a width of 1 to 10 cm inthe entry zone of the channels and wherein the width of the channels atleast doubles between the entry thereof and the exit thereof

BACKGROUND OF THE INVENTION

The removal of volatile components from a polymer solution is one of thefinal processing stages in the production of many polymers. The volatileconstituents to be removed may be either solvents or unpolymerisedmonomers. Depending upon the viscosity of the polymer solution, variousmethods are known for the removal of the volatile components frompolymer solutions, each involving heating the polymer solution by meansof a heat exchanger to a temperature above the vaporisation temperatureof the volatile constituents. Drying devices which are described are,for example, film evaporators, extruders and those with indirect heatexchange.

It is vital during heating of the polymer solution that the polymer isnot thermally degraded.

Published patent application EP-A-150225 describes an apparatus havingtwo heat exchange bundles connected in series. The heat exchange bundleshave rectangular channels. This apparatus is primarily used fortwo-stage heating or cooling during the reaction, but is a relativelycomplex piece of equipment. EP-B-226204 discloses a process and a heatexchanger for the removal of volatile constituents from a polymersolution containing at least 25 wt. % of polymer. The polymer solutionis heated in an indirect heat exchange zone, which consists of aplurality of channels. The channels have a substantially uniform ratioof surface area to volume in the range from 0.158 to 1.97 mm⁻¹, a heightof 1.27 to 12.7 mm, a width of 2.54 to 10.16 cm and a length of 1.27 to30.48 cm. The polymer solution is heated in the channels at a pressureof 2-200 bar to a temperature above the vaporisation temperature of thevolatile components, but below the boiling temperature of the polymer.The residence time of the polymer solution in the channels is 5 to 120seconds. After heating, the solution is transferred into a chamber inwhich at least 25% of the volatile constituents are stripped from thesolution. The process reduces thermal damage by reducing the time forwhich the polymer is exposed to elevated temperatures. One disadvantageof the process is, however, that it is not possible to achieve completeremoval of the solvent in a single stage. Moreover, polymer depositsform on the outside of the heat exchange bundle which carbonise overtime and occasionally flake off, so contaminating the polymer from whichthe solvent has been removed.

EP-B-352 727 discloses a process for the removal of volatileconstituents from polymer solutions by heating the polymer solution toabove the vaporisation temperature of the volatile components in aplurality of channels connected in parallel. The ratio of heat exchangesurface area to the volumetric flow rate of the product is ˜80 m²/m³/h.The flow velocity in the channels is ˜0.5 mm/s and the residence time ofthe polymer solution in the channels is 120 to 200 seconds. This processalso has the disadvantage that complete removal of the solvent is notpossible in a single stage. Moreover, polymer deposits form on theoutside of the heat exchange bundle which carbonise over time andoccasionally flake off, so contaminating the polymer from which thesolvent has been removed.

The object thus arises of providing an apparatus and a process for theremoval of volatile components from a polymer solution which do notexhibit the disadvantages of the prior art.

DETAILED DESCRIPTION OF THE INVENTION

The object is achieved by providing a device of the present inventionfor the removal of volatile components from a polymer solutioncomprising at least a container (30), which has an inlet (1) for thepolymer solution, an outlet (3) for the volatile components and anoutflow (2) for the polymer solution from which the volatile componentshave been removed, and a heat exchanger (31), which is arranged insidethe container (30), with a central receiving zone (21) for the polymersolution, which is connected to the container inlet, a product zone (18)to receive the treated polymer solution, a heat exchange unit (31)having a plurality of channels (14), which form a heat exchange zone andwhich connect the receiving zone to the product zone (18), a heatingmeans (13) to heat the heat exchange unit (31) and the channels,characterized in that the channels (14) have a length of 1.0 to 40 cm, aheight, constant over the length thereof, of 1.3 to 13 mm and a width of1 to 10 cm in the entry zone of the channels (14) in the receiving zone(21), wherein the width of the channels (14) at least doubles betweenthe entry (23) thereof and exit (32) thereof to the product zone (18).

The present invention provides a device for the removal of volatilecomponents from a polymer solution comprising at least one container,which has an inlet for the polymer solution, an outlet for the volatilecomponents and an outflow for the polymer solution from which thevolatile components have been removed, and a heat exchanger arrangedinside the container which has a central receiving zone for the polymersolution, which is connected to the container inlet, a product zone toreceive the treated polymer solution, a heat exchange unit having aplurality of channels, which form a heat exchange zone and which connectthe receiving zone to the product zone, a heating means to heat the heatexchange unit and the channels, characterised in that the channels havea length of 1.0 to 40 cm, a height, constant over the length thereof, of1.3 to 13 mm and a width of 1 to 10 cm in the entry zone of the channelsin the receiving zone, wherein the width of the channels at leastdoubles between the entry thereof and the exit thereof to the productzone.

The channels preferably have a rectangular cross-section and the widthof the channels at the outlet is three times as large as the width ofthe channels at the inlet, wherein the channels may widen continuously,but in accordance with any desired profile.

In a preferred embodiment, the channels widen parabolically.

A device in which the width of the channels is kept constant for atleast half the length thereof and then widens to at least double thewidth, wherein the enlargement proceeds continuously, but in accordancewith any desired, in particular non-linear, profile is likewisepreferred. When an appropriately adjusted temperature is used, thechannel shapes ensure that the width of the channel is constant in thezone in which the polymer solution is heated and does not enlarge untilthe polymer solution has reached a temperature of above the vaporisationtemperature of the volatile components, such that these may readily bestripped out of the solution while still in the channels.

In one variant, both the width and the height of the channel may widentowards the exit in the preferred manner.

The heat exchanger of the device according to the invention preferablyhas at least 100 such channels. In particular, however, there are 200 to100,000 channels in the heat exchanger.

In a preferred embodiment, the heat exchanger has a cylindrical shape,such that the channels surround the receiving zone in a cylindricalconfiguration. The heat exchanger is preferably arranged in the area ofthe channel outlets that the individual channels directly abut with eachother laterally and/or at the upper and under side thereof, such thatthere are no zones between the channel exits on which the polymermaterial may be deposited. This applies to both the cylindrical and anyother configuration of the channels.

In another preferred embodiment of the device, the heat exchange unit inparticular has a cuboid shape and is arranged beneath the receivingzone.

In a preferred embodiment, the heat exchange unit is formed from aplurality of superposed or adjacent plate segments arranged in planes,wherein the plate segments are spaced apart in one plane, and whereinthe spacing thereof and the lateral profile in the plane determine thewidth of the channels and the thickness of the plate segments determinesthe height of the channels.

In a preferred variant of the device, the heat exchange unit is formedfrom a plurality of superposed or adjacent plates arranged in planes,which plates are separated by spacers, wherein the spacing and lateralprofile of the spacers determine the width of the channels and thethickness of the spacers determines the height of the channels.

The device is preferably entirely or in part, in particular those partsin contact with the polymer solution, made from a metallic materialhaving a low iron content which contains at most 10 wt. %, preferably atmost 5 wt. % of iron.

The material having a low iron content is preferably tantalum or anickel alloy having a low iron content and is in particular selectedfrom the range Alloy 59 (2.4605), Inconell 686 (2.4606), Alloy-B2,Alloy-B3, Alloy-B4, Hastelloy C-22, Hastelloy-C276, Hastelloy-C4,preferably Alloy 59.

The heat exchanger has any desired means known to the person skilled inthe art for heating the channels to temperatures above the vaporisationtemperature of the volatile components. These means are, for example,resistance heaters or a network of tubes to convey a heat exchangefluid.

The channels in the heat exchange unit are preferably inclined over thelength thereof by a downwards angle relative to the horizontal towardsthe exit thereof, in particular, they are arranged vertically. In thiscase, the receiving zone is arranged above the channels.

The heating means for the heat exchanger preferably comprise a pluralityof tubes which pass transversely relative to the channels through theplate segments or through the plates and through which a heat exchangefluid circulates.

The present invention also provides a process for the removal ofvolatile components from a polymer solution containing at least 40 wt. %of polymer using the device according to the invention, wherein theprocess comprises:

A) introduction of the polymer solution into the receiving zone at apressure of 1 to 100 bar abs.,

B) passage and heating of the polymer solution in the channels of theheat exchanger to a temperature above the vaporisation temperature ofthe volatile components of the polymer solution and below the boiling ordecomposition temperature of the polymer, wherein the residence time ofthe polymer solution in the channels is from 5 to 120 sec,

C) separation of the volatile components from the polymer solutionthrough the outlet and

D) discharge of the polymer from which the volatile components have beenremoved.

The device and process according to the invention may be generallyapplied for the removal of volatile components from sensitive solids, inparticular from thermoplastic polymers, elastomers, silicone polymersand high molecular weight lubricants and similar substances.

Preferably, however, the process according to the invention is used fordegassing thermoplastic polymers. These polymers comprise any plasticswhich flow under the action of pressure and heat. Polystyrene,polycarbonate, polyphenylene, polyurethane, polyamide, polyester,polyacrylate, polymethacrylate may be mentioned by way of example inthis connection. The process is very particularly suitable for degassingpolycarbonate.

The volatile components may be both unpolymerised monomers and solvents.One solvent frequently used in the production of thermoplastic polymersis, for example, methylene chloride, or a mixture of methylene chlorideand chlorobenzene.

The polymer solutions contain at least 40 wt. % of polymer. In themolten state, the polymer solution typically has a viscosity of 0.5 to200 Pas.

In the process, the polymer solution is in particular compressed intothe channels at a pressure of 1.5 to 50 bar abs., preferably of 2 to 5bar abs., flows through the channels of the heat exchanger and is soheated to a temperature of preferably 250 to 350° C. The pressureprevailing at the outlet of the channels is preferably below thesaturation pressure of the volatile components at the particulartemperature. The pressure in the product zone is preferably less than orequal to 10⁵ Pa, in particular from 3000 Pa to 10⁵ Pa.

Preferably, the pressures upstream and downstream from the channels, thetemperature in the channels and the shape of the channels are selectedsuch that the volatile components are already completely separated fromthe polymer in the channels.

The pressure in the receiving zone and the temperature in the channelsis in particular selected such that at least 95%, in particular at least98%, preferably at least 99.5%, particularly preferably at least 99.8%of the volatile components of the polymer solution vaporise in thechannels.

The residence time of the polymer solution in the channels is typically5 to 120 sec, preferably 80 to 120 sec. The flow velocity of the polymersolution is in particular from 0.0001 to 0.01 mm/s, preferably from0.001 to 0.005 mm/s. The ratio of heat exchange surface area of thechannels to the volumetric flow rate of the polymer solution is 5 to 75,preferably 15 to 50 m²/m³/h.

BRIEF DESCRIPTION OF THE FIGURES

The following Figures illustrate the invention in greater detail. Theseillustrations are provided merely by way of example and thus do notlimit the invention.

FIG. 1 shows a longitudinal section of an apparatus according to theinvention.

FIG. 2 shows a preferred arrangement of the channel width.

FIG. 3 shows a cross-section of one plane of the heat exchanger.

FIG. 4 shows in a longitudinal section through one part of a heatexchanger how the planes of the heat exchanger are superposed.

FIG. 5 shows a cross-section through one part of a variant of the heatexchanger of a device according to the invention comprising superposedplate segments.

FIG. 6 shows a longitudinal section through a variant of the deviceaccording to the invention having vertically arranged channels.

FIG. 7 shows a longitudinal section along line A—A in FIG. 6 insimplified form to clarify the passage of the heat exchange mediumthrough the tubes 13.

EXAMPLES

The apparatus according to the invention is represented in FIG. 1. Allunits are made from Alloy 59 or have an Alloy 59 coating. The apparatushas a double shell 16. The upper part of the apparatus has an inlet 1for the polymer solution and an outlet 3 for the volatile components. Inthe lower part, the polymer from which the volatile constituents havebeen removed is discharged through the outlet 2 with the assistance ofpump 24. The temperature of the inlet 1 is controlled with a heatexchange medium.

Inside the double shell 16 is located the heat exchanger 31 with acentral receiving zone 21 to receive the polymer solution to bedegassed. The receiving zone 21 is connected to the inlet 1. 200channels 14 (cf. FIG. 2) are arranged around the receiving zone 21,which channels extend from the receiving zone to the periphery of theheat exchanger 31 and which flare parabolically towards the exit 32 intothe product zone 18.

The polymer solution is pumped through the inlet 1 into the receivingzone 21 using a conventional pump (not shown). In order to achieve amore uniform distribution of the polymer solution into the individualchannels, a cylindrical displacement member 10 is located in the centreof the receiving zone 21. The heat exchanger furthermore has means toheat the channels to above the vaporisation temperature of the volatilecomponents. These means are a plurality of tubes 13 on the periphery orwithin the heat exchanger 31, which are interconnected by the annularchamber 17. In the upper part, the tubes 13 are connected to the annularchamber 11, in which the hot heat exchange oil is introduced throughline 4. The heat exchange oil is discharged from the heat exchangerthrough the line 5. The tubes 13 are held together by end plates. Theshell 16 of the apparatus may be heated with a heat exchange fluid.

FIG. 2 is a schematic representation of a longitudinal section of achannel according to the invention of the device. The entry 23 has arectangular cross-section with a height of 2 mm and a width of 10 mm.The length of the channel is 110 mm. The width of the channel is aconstant 10 mm for the first 60 mm. Thereafter, the channel widens, suchthat the width thereof at the exit 32 is 40 mm. The downstream portionof the side walls 25 and 26 of the channel 14 is parabolic in shape.

FIG. 3 shows how the channels 14 according to the invention are arrangedin a circular configuration around the receiving zone 21. The tubes 13run through the holes 22 in the spacers 20.

FIG. 4 shows a longitudinal section of several superposed channelplanes. The channels 14 are formed by a plurality of alternatelysuperposed spacers 20 and plates 19, through which the tubes 13 pass andhold the spacers and the plates in position. The arrangement shown hereis suitable for a device having a vertical position of the channels 14.The receiving zone 21 in this case is located above the channel entries23.

In the variant shown in FIG. 5, the heat exchange unit 31 is formed bylayers 37 of superposed plate segments 36. The segments 36 are spacedapart by a layer 37 and so form the width of the channels 14. The heightof the channels 14 is defined by the thickness of the plate segments 36.

The functioning of the apparatus according to the invention is furtherillustrated by means of FIG. 1. Once the polymer solution to be treatedhas been conveyed into the receiving zone 21, the solution passes intothe channels 14, in which it is heated and the volatile components areremoved therefrom. At the end 32 of the channels 14, the degassedpolymer falls due to gravity into the product zone 18 of the shell 16and is conveyed out of the apparatus according to the invention by meansof pump 24 via line 2. The volatile components are drawn off through theoutlet 3. The channels are heated by a heat exchange fluid, whichcirculates in the lines 4, 13 and 5.

In the variant of the device according to FIG. 6 (longitudinal section),vertically arranged layers of rectangular plates 19 and spacers 20 (cfFIG. 4) are held together by a bundle of tubes 13, the ends of which areconnected by tube bends (not shown) and form a tubing system. The tubingsystem is connected to the inlet tube 4 and the outlet 5 for passage ofa heat exchange oil (cf FIG. 7).

The polymer solution enters the device through the inlet 1 (FIG. 6),passes through the receiving zone 21 with the displacement member 10 andis distributed among the channels 14. In the channels 14, the solutionflows downwards and the volatile constituents are removed by heating.The polymer melt leaves the channels 14 and drips into the product zone18 for further processing. The polymer is discharged by means of thepump 24 through the line 2.

Test Example

In this Example, a 75 wt. % polycarbonate solution containing 24 wt. %of chlorobenzene and 1 wt. % of methylene chloride was concentrated inan apparatus as shown in FIG. 1. The polycarbonate solution wascompressed into the channels 14 at a pressure of 3000 hPa and heatedtherein to 300° C. A pressure of 40 hPa prevailed in the product zonedownstream from the channels. The residence time of the polymer in thechannels 14 was 100 seconds. The channels were 1 cm wide at the entry 23and 3 cm wide at the exit 32 and, after half the channel length, flareout as shown in FIG. 2. All parts in contact with the product were madefrom Alloy 59. The pressures at the entry 23 and exit 32 of the channels14 and the shape of the channels were selected such that the volatilecomponents have already completely or at least virtually completely beenremoved in the channels. The degassed polycarbonate exhibited a residualchlorobenzene content (solvent) of only 400 ppm.

What is claimed is:
 1. In a device for removing volatile components froma polymer solution comprising a container comprising: (i) an inlet forthe polymer solution; (ii) an outlet for the volatile components; (iii)an outflow for the polymer solution from which the volatile componentshave been removed; (iv) a heat exchange unit arranged inside thecontainer with a central receiving zone for the polymer solution, thecentral receiving zone connected to the container inlet; and (v) aproduct zone to receive the polymer solution from which the volatilecomponents have been removed, wherein the heat exchange unit has aplurality of channels forming a heat exchange zone and connecting thecentral receiving zone to the product zone, the improvement comprisingincluding a heating means to heat the heat exchange unit and thechannels, wherein the channels have a length of 1.0 to 40 cm, a height,constant over the length thereof, of 1.3 to 13 mm and a width of 1 to 10cm at entry of the channels and wherein the width of the channels atleast triples between the entry and the exit thereof to the productzone.
 2. In a device for removing volatile components from a polymersolution comprising a container comprising: (i) an inlet for the polymersolution; (ii) an outlet for the volatile components; (iii) an outflowfor the polymer solution from which the volatile components have beenremoved; (iv) a heat exchange unit arranged inside the container with acentral receiving zone for the polymer solution, the central receivingzone connected to the container inlet; and (v) a product zone to receivethe polymer solution from which the volatile components have beenremoved, wherein the heat exchange unit has a plurality of channelsforming a heat exchange zone and connecting the central receiving zoneto the product zone, the improvement comprising including a heatingmeans to heat the heat exchange unit and the channels, wherein thechannels have a length of 1.0 to 40 cm, a height, constant over thelength thereof, of 1.3 to 13 mm and a width of 1 to 10 cm at entry ofthe channels and wherein the width of the channels is constant betweenthe entry and at least half the length thereof and at least doubles overthe remainder of the length thereof to the exit to the product zone. 3.In a device for removing volatile components from a polymer solutioncomprising a container comprising: (i) an inlet for the polymersolution; (ii) an outlet for the volatile components; (iii) an outflowfor the polymer solution from which the volatile components have beenremoved; (iv) a heat exchange unit arranged inside the container with acentral receiving zone for the polymer solution, the central receivingzone connected to the container inlet; and (v) a product zone to receivethe polymer solution from which the volatile components have beenremoved, wherein the heat exchange unit has a plurality of channelsforming a heat exchange zone and connecting the central receiving zoneto the product zone, the improvement comprising including a heatingmeans to heat the heat exchange unit and the channels, wherein thechannels have a length of 1.0 to 40 cm, a height, constant over thelength thereof, of 1.3 to 13 mm and a width of 1 to 10 cm at entry ofthe channels and wherein the width of the channels increasesnon-linearly between the entry and exit thereof to the product zone. 4.The device according to claim 3, wherein the width of the channelsincreases parabolically.
 5. The device according to any one of claims1-3, wherein the heat exchange unit comprises more than 100 channels. 6.The device according to any one of claims 1-3, wherein the heat exchangeunit has a cylindrical shape and surrounds the receiving zone.
 7. Thedevice according to any one of claims 1-3, wherein the heat exchangeunit has a cuboid shape and is arranged beneath the receiving zone. 8.The device according to any one of claims 1-3, wherein the heat exchangeunit is formed from a plurality of superposed or adjacent plate segmentsarranged in planes, wherein the plate segments are spaced apart in oneplane and wherein the spacing thereof and the lateral profile in theplane determine the width of the channels and the thickness of the platesegments determines the height of the channels.
 9. The device accordingto any one of claims 1-3 wherein the heat exchange unit is formed from aplurality of superposed or adjacent plates arranged in planes, whichplates are separated by spacers, wherein the spacing and lateral profileof the spacers determine the width of the channels and the thickness ofthe spacers determines the height of the channels.
 10. The deviceaccording to any one of claims 1-3, wherein the channels in the heatexchange unit are inclined over the length thereof by a downwards anglerelative to the horizontal towards the exit thereof.
 11. The deviceaccording to any one of claims 1-3, wherein the heating means comprisesa plurality of tubes which pass transversely relative to the channelsthrough plates or plate segments and through which a heat exchangeliquid circulates.
 12. The device according to any one of claims 1-3,wherein the device at least partially comprises a metallic materialcontaining at most 10 wt. % of iron.
 13. The device according to claim12, wherein the metallic material is tantalum or a nickel alloy having alow iron content and is selected from the group consisting of Alloy 59(2.4605), Inconell 686 (2.4606), Alloy-B2, Alloy-B3, Alloy-B4, HastelloyC-22, Hastelloy-C276 and Hastelloy-C4.
 14. The device according to claim12, wherein the metallic material comprises Alloy
 59. 15. A process forthe removal of volatile components from a polymer solution containing atleast 40 wt. % polymer comprising: (a) providing a device for removingvolatile components from said polymer solution comprising a containercomprising, (i) an inlet for the polymer solution, (ii) an outlet forthe volatile components, (iii) an outflow for the polymer solution fromwhich the volatile components have been removed, (iv) a heat exchangeunit arranged inside the container with a central receiving zone for thepolymer solution, the central receiving zone connected to the containerinlet, and (v) a product zone to receive the polymer solution from whichthe volatile components have been removed, wherein the heat exchangeunit has a plurality of channels forming a heat exchange zone andconnecting the central receiving zone to the product zone, theimprovement of said device comprising including a heating means to heatthe heat exchange unit and the channels, wherein the channels have alength of 1.0 to 40 cm, a height, constant over the length thereof, of1.3 to 13 mm and a width of 1 to 10 cm at entry of the channels, andwherein one of, (I) the width of the channels at least triples betweenthe entry and the exit thereof to the product zone, (II) the width ofthe channels is constant between the entry and at least half the lengththereof and at least doubles over the remainder of the length thereof tothe exit to the product zone, and (III) the width of the channelsincreases non-linearly between the entry and exit thereof to the productzone; (b) introducing the polymer solution into the central receivingzone at a pressure of 1 to 100 bar abs.; (c) passing and heating thepolymer solution in the channels of the heat exchanger to a temperatureabove the vaporization temperature of the volatile components of thepolymer solution and below the boiling or decomposition temperature ofthe polymer, wherein the residence time of the polymer solution in thechannels is from 5 to 120 seconds; (d) separating the volatilecomponents from the polymer solution through the outlet; and (e)discharging the polymer from which the volatile components have beenremoved.
 16. The process according to claim 15, wherein the polymer is athermoplastic polymer selected from the group consisting of polystyrene,polyphenylene, polyurethane, polyamide, polyester, polyacrylate,polymethacrylate, polycarbonate, a copolymer of the stated polymers andan elastomer or a silicone polymer.
 17. The process according to claim15, wherein the volatile component is a polymer solvent or a monomer ofthe polymer.
 18. The process according to claim 15, wherein the pressurein the receiving zone and the temperature in the channels are selectedsuch that at least 95% of the volatile components of the polymersolution vaporize in the channels.
 19. The process according to claim18, wherein the pressure and temperature are selected such that at least98% of the volatile components of the polymer solution vaporize in thechannel.
 20. The process according to claim 18, wherein the pressure andtemperature are selected such that at least 99.5% of the volatilecomponents of the polymer solution vaporize in the channel.
 21. Theprocess according to claim 15, wherein the temperature in the channelsis 250 to 350° C.
 22. The process according to claim 15, wherein thepressure in the receiving zone at the entry to the channels is from 1.5to 50 bar abs.
 23. The process according to claim 15, wherein thepressure in the product zone is less than or equal to 10⁵ Pa.
 24. Theprocess according to claim 15, wherein the pressure in the receivingzone at the entry to the channels is from 2-5 bar abs.
 25. The processaccording to claim 15, wherein the pressure in the product zone is from3000 to 10⁵ Pa.